AUSTIN — Teenagers who believe people can’t change react more aggressively to peer conflicts than those who think people can change. And teaching them that people have the potential to change can reduce these aggressive reactions, according to a new psychology study from The University of Texas at Austin.

The study, published in the February 2013 issue of Child Development, has important implications for bullying interventions in public schools.

“When adolescents believe the world is full of ‘good’ and ‘bad’ people, with nobody in between, they are then quick to classify people as one or the other,” said David Yeager, assistant professor of developmental psychology at The University of Texas at Austin. “We found that teens in this ‘fixed’ mindset — even after a minor offense like getting bumped in the hall or being left out of a game of catch — relegated peers to the ‘bad person’ group, decided that they had offended on purpose and wanted aggressive revenge.”

Yeager and a team of researchers from Emory University and Stanford University conducted eight studies with more than 1,600 eighth- through 10th-graders of different races and ethnicities in wealthy and low-income schools across the United States.

Teens reported their beliefs about change — for instance, whether bullies and victims are types of people who can’t change — and then responded to situations of conflict or exclusion. Across the board, respondents who believed people can’t change were more likely to think the offense was done on purpose, and as a result desired aggressive revenge to “hurt them” or “punish them.”

Next, the researchers developed and tested a brief intervention that taught the teens about the potential for change in people. Students read an article about the plasticity of the brain, read notes from older students describing how people are capable of change, and then wrote notes to future students on this topic to make the message stick. The teens were then asked to respond to a hypothetical offense.

The intervention reduced the respondents’ tendency to see the offense as having been done on purpose and reduced their desire for aggressive revenge even eight months after the students took part in the study.

A related studyled by Yeager, which was published in the October 2012 online issue of Child Development, showed that a longer version of the program could reduce actual behavioral aggression at a low-income urban public high school over an extended period.

“Usually when the public thinks about aggression, we mainly think about violent environments as causes,” Yeager says. “And then we think that by the high school years, this aggression is deeply ingrained. We don’t often realize that changing a simple belief can also affect aggression.”